Add comprehensive scheduling functionality with reminder notifications:
- Add scheduledDate, scheduledTime, and reminderMinutes fields to ImmerseTask
- Add enableReminders and defaultReminderMinutes to plugin settings
- Implement reminder notification system with 30-second background checks
- Add overdue task detection with visual indicators
- Add native HTML5 date/time pickers in Quick Add and Edit modals
- Add reminder dropdown with 5/10/15/30/60 minute options
- Display scheduled date/time with blue badge (📅) in task list
- Show pulsing red "OVERDUE" badge (⚠️) for past-due tasks
- Add red left border highlight for overdue tasks
- Implement startup check for due/overdue tasks when plugin loads
- Show overdue notices when Obsidian opens if tasks are past due
- Play alert sounds for reminders (if sounds enabled)
- Track shown reminders to prevent duplicate notifications
